1. Field of the Invention
This invention relates generally to catheters and in particular to a thermal angioplasty catheter.
2. Description of the Prior Art
Percutaneous transluminal balloon angioplasty (PTA) has become an established technique for treating atherosclerotic occlusive disease. The principle of intraluminal dilitation of arterial plaque was described by Dotter in 1964. Dotter, C.T., et al., "Transluminal Treatment of Arteriosclerotic Obstruction: Description of a New Technique and a Preliminary Report of Its Application," Circulation (1964) 30:654. The treatment, however, was not widely accepted until the discovery of nonelastomeric balloons followed by the discovery of angiographic techniques for transluminal balloon angioplasty by Gruntzig in 1976. Gruntzig, R. A., et al., "Nonoperative Dilation of Coronary Artery Stenosis: Percutaneous Transluminal Coronary Angioplasty," New England Journal of Medicine (1979) 301:61.
The PTA technique utilizes a catheter that has a small diameter (typically 4 French to 8 French) and is equipped with an expandable chamber similar to a balloon. The chamber is concentric to the catheter and is located near the distal end of the catheter. The catheter is introduced into the appropriate blood vessel and is advanced through the vessel lumen to a narrowing of a blood vessel caused by atheromatous mass. The deflated balloon is positioned at the site of the atheromatous plaque. The balloon is inflated in a controlled manner by injection of an appropriate fluid, compacting the atheromatous mass. After the balloon is deflated, the blood vessel has a larger luminal diameter, thereby improving blood flow.
As a result of the high percentage of initially successful dilitations, transluminal balloon angioplasty has gained widespread acceptance. However, a significant recurrence rate of 30 percent, has been observed at the time of follow-up angiograms as reported by Meier and King. Meier, B., King, S., "Repeat Coronary Angioplasty," Journal of American Colleqe of Cardioloov (1984) 55:463. For this reason, other methods have been developed for the dilitation or removal of atheromatous plaque.
One method for the removal of atheromatous plaque utilizes a catheter incorporating an optical fiber for the transmission of laser energy to the distal portion of catheter and into the stenosed arteries. Using this technique, the stenosed arteries are recanalized by the application of laser energy to ablate or vaporize the atheromatous mass. One disadvantage of this method is the widespread thermal injury to the arterial wall resulting in arterial perforation, aneurysm formation and thrombosis. Another limitation of laser ablation methods is that calcified plaques cannot be vaporized but are often fragmented by acoustic shock waves created by the pulsed laser interaction with the plaque. When such fragmentation occurs, there is an increased potential for embolization.
An alternative method for recanalization of obstructed arteries has also been developed by Spears (see European Patent No. EP-85402067) and involves the filling of the balloon (used to expand the obstructed artery) with a liquid which has a high absorbance of laser light. The laser light is then transmitted to the balloon from an external laser source via a fiber optic within the angioplasty catheter. The liquid contained within the balloon is heated by the laser energy. This heating serves to minimize reclosure following conventional balloon angioplasty. Other methods of heating the fluid (e.g., water or water containing dye) in the balloon are also suggested by Spears including exothermic (chemical) reactions and resistance heating of fluid contained within the balloon.
Another method for supplying heat to the tip of the balloon angioplasty catheter has been suggested by Cumberland, et al. Cumberland, D.C., "Percutaneous Laser Thermal Angioplasty: Initial Clinical Results with a Laser Probe in Total Peripheral Artery Occlusions," Lancet (June 28, 1986) pp. 1457-1459. This technique utilizes a metal tip at the distal portion of the catheter. The metal tip is heated to about 400 C. by use of argon laser to recanalize occluded blood vessels.
Another method for recanalizing occluded blood vessels suggested by Kensey, et al., removes atheromatous plaque by using a rotating tip catheter to "drill" or bore through the occlusive mass. Kensey, et al., "Abstracts of the 59th Scientific Sessions, Circulation (1986) 74(II):11.
Another method of opening the stenosed blood vessel is described by Simpson, et al. Simpson J. B., et al., "Transluminal Atherectomy--Initial Clinical Results in 27 Patients," Circulation (Oct. 1986) 74 (II):4; "Transluminal Coronary Atherectomy (TCA), Results in 21 Human Cadaver Vascular Segments," Circulation (Oct. 1986) 74 (II):4; Faxon, D.P., et al., "In Vivo Evaluation of Atherectomy, A New Technique to Enlarge Atherosclerotic Vessels,"Circulation (Oct. 1985) 72 (II):4. In this method, a catheter device is used to cut and retrieve the occluding plaque from the artery. The catheter consists of a boat shaped metal housing, containing a high speed rotating cutter, and a balloon attached to the opposite side on the housing. The device is positioned at the site of the atherosclerotic narrowing in the artery, and the balloon is inflated to press the plaque into the opening of the housing. The rotating cutter is then advanced forward thereby cutting the atheroma which is protruding into the housing. The excised plaque is retrieved from the housing when the catheter is removed from the blood vessel. In this method, the lumen of the blood vessel is enlarged by cutting and removing the plaque which is occluding the blood flow. There are two main limitations of this method. First, the housing, made from a rigid material, can not be positioned safely in blood vessels at the site of a curve, as well as the sites of "high grade lesions" (i.e. small luminal openings). The second limitation of this device is that it removes the material in the longitudinal direction of the artery, creating a "channel" in the lumen. One has to create a number of these channels in the lumen circumferentially to more effectively treat the atherosclerotic disease in the artery.